Thesis (Ph. D.)--Worcester Polytechnic Institute. / Keywords: hydrodechlorination; reaction kinetics; reaction steps; chlorinated compounds; Palladium catalysts. Includes bibliographical references.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20205号 / 理博第4290号 / 新制||理||1616(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 依光 英樹, 教授 大須賀 篤弘, 教授 丸岡 啓二 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

" Hydrodechlorination is the reaction of a chlorinated organic compound (R-Cl) with hydrogen to form a carbon-hydrogen bond and HCl: R-Cl + H2 = R-H + HCl. This reaction is used in refrigerant manufacturing, industrial by-product reclamation and waste management. These practical applications require in-depth understanding of hydrodechlorination reaction. In this research work, we studied four families of chlorinated compounds; CF3CF3-xClx(x=1-3), CH4-xClx (x=1-4), CF4-xClx (x=1-4) and dichloropropanes (1,1-, 1,2-, 1,3-, 2,2-), on supported palladium catalysts to create a theory capable of predicting the hydrodechlorination rate on chlorinated compounds and to explore the reaction mechanism. A possible set of elementary reaction steps of hydrodechlorination reaction was proposed from our kinetics study of all these compounds. In this set of reaction steps, the irreversible scission of the first C-Cl bond in a chlorinated compound was proposed to be the rate-determining step; gas phase H2 and HCl were suggested to be in equilibrium with surface H and Cl species; adsorbed Cl was assumed to be the most abundant surface intermediate. The overall rate of hydrodechlorination reaction could be derived from these reaction steps as r=k'[R-Cl]/(1+K'[HCl]/[H2]0.5). In this rate equation, k'is the product of the adsorption equilibrium constant of the chlorinated compound on catalyst surface times the rate constant for the scission of the first C-Cl bond scission step, and K'is the square root of the equilibrium constant for the equilibrium between H2, HCl and their corresponding surface species: 2HCl + 2* = H2 + 2Cl*. The hydrodechlorination reaction of CF3CFCl2 was performed in the presence of H37Cl to study the reversibility of C-Cl bond scission, and the removal of the first Cl atom from CF3CFCl2 was found to be an irreversible step. Hydrodechlorination experiments of CF3CFCl2 with D2 and HCl mixture revealed that D2 and HCl were in equilibrium with surface adsorbed hydrogen and chlorine during reaction. The forward rate and reverse rate of this equilibrium were at least 400 times higher than the overall hydrodechlorination rate. This result supported the assumption of equilibrium for 2HCl + 2* = H2 + 2Cl*. Additionally, the activation energy for the rate determining step was extracted from hydrodechlorination reaction kinetics results of CH4-xClx (x=1-4), CF4-xClx (x=1-4) and dichloropropanes (1,1-, 1,2-, 1,3-, 2,2-) compounds. It was found that for each of the series compounds, a linear relationship existed between C-Cl bond scission activation energy and gas phase C-Cl bond strength. This observation corroborates our assumption that the removal of the first Cl atom from a chlorinated compound is the rate-determining step in the hydrodechlorination reaction. Thus, all kinetic and isotope experimental results obtained from this study are consistent with the proposed reaction steps for the chlorinated compounds tested. This set of reaction steps can also be used to predict the hydrodechlorination reaction rate of a chlorinated compound, once its gas phase C-Cl bond energy is calculated and the turnover rate of a reference chlorinated compound with similar structure is known. Some work has been done to study hydrodechlorination reaction steps and reaction intermediates beyond the rate-limiting step. Isotope tracing experiments with D2 indicated that CH3-, CH2- groups adjacent to a C-Cl bond could undergo deuterium exchange. The study of reactions steps using ab initio methods, including calculation of rate constants, is also under way. Calculations for the CH4-xClx (x=1-4) family showed that the heat of adsorption and C-Cl bond dissociation energy on a Pd surface were linearly related to their gas phase C-Cl bond strength."

A reação de hidrodescloração (HDC) tem recebido grande atenção como um método de tratamento de resíduos orgânicos mais eficiente que a incineração, especialmente para compostos aromáticos clorados, pois evita a formação de espécies potencialmente tóxicas, como furanos e dioxinas. O presente estudo tem como objetivo a preparação de nanocatalisadores de paládio suportados para a reação de HDC. Buscando facilitar a separação do catalisador do meio reacional e sua reutilização em sucessivas reações foram empregados suportes sólidos com propriedades magnéticas e desenvolvidas estratégias para a imobilização de nanopartículas metálicas nestes suportes. Para isso foi preparado um suporte composto por nanopartículas magnéticas revestidas por uma camada protetora de sílica densa. Os núcleos magnéticos foram preparados pelo método da coprecipitação e em seguida recobertos com sílica pelo método da microemulssão reversa. A estratégia usada para a preparação das nanopartículas de paládio suportadas foi a funcionalização da superfície do suporte, a imobilização do precursor de Pd(II) e a subseqüente redução do metal por hidrogênio em condições brandas. Como resultado foram obtidas nanopartículas de Pd bem dispersas no suporte funcionalizado, sendo que o tamanho de partícula foi dependente do grupo funcional presente no suporte. Suportes funcionalizados com amina e etilenodiamina resultaram em nanopartículas de Pd com diâmetro de 6,4 ± 1,4 nm e 1,3 ± 0,3 nm, respectivamente. Em testes catalíticos de hidrogenação de cicloexeno o catalisador amino-funcionalizado apresentou melhor desempenho com relação ao funcionalizado com etilenodiamina. Para a reação de HDC foram estudadas as melhores condições reacionais para obtenção de uma maior taxa de conversão do substrato, preservando a estrutura do catalisador. Clorobenzeno foi empregado como substrato modelo. Os testes preliminares em diferentes bases e solventes sugeriram que a trietilamina em isopropanol é o melhor meio por resultar em boa conversão de substrato sem alteração significativa na estrutura do suporte após a reação. O lixiviamento dos metais, nos casos estudados, não foi relevante em relação à quantidade de metal presente inicialmente no suporte. As reações em tampão acetato e carbonato também resultaram em boas taxas de conversão, sendo que no teste de reuso o catalisador começou a diminuir a atividade apenas no quarto reciclo. O meio tamponado é uma alternativa interessante por ser menos agressiva, mas ainda muito pouco explorada para a reação de HDC. / The hydrodechlorination reaction (HDC) has received great attention as an alternative treatment of organic residues, which is more efficient than incineration, especially for aromatic organic compounds, and avoids the formation of toxic species, such as furans and dioxins. The present study is focused on the preparation of supported palladium nanocatalysts for HDC. In order to facilitate the separation of the catalyst from the reaction medium and its reuse in successive reactions solid supports with magnetic properties were employed and strategies for the immobilization of metal nanoparticles on the surfaces of these supports were developed. For this purpose a catalyst support comprised of magnetic nanoparticles coated by a protective dense silica layer was developed. The magnetic nuclei were prepared by the co-precipitation method followed by silica coating by a reverse microemulsion. The strategy used for the preparation of supported Pd nanoparticles was first the functionalization of the support surface, immobilization of Pd (II) precursors and than metal reduction by hydrogen under mild conditions. As a result, Pd nanoparticles well-dispersed on the functionalized support were obtained, although the size of the Pd nanoparticles was tuned by the ligand grafted on the support surface. Amine and ethylenediamine functionalized supports formed Pd nanoparticles of 6,4 ± 1,4 nm and 1,3 ± 0,3 nm, respectively. In the catalytic tests of ciclohexene hydrogenation, the amino-functionalized catalyst showed the best performance compared to the ethylenodiamine functionalized support. For the HDC reaction, the most favorable reaction conditions to reach the highest substract conversion rates while preserving the catalyst structure were studied. Chlorobenzene was selected as substrate for the HDC experiments. Initial tests using different bases and solvents suggested that triethylamine in isopropanol are the best conditions for good conversion rates without meaningful change in the support structure after reaction. The metal leaching was negligible in all reactions studied with respect to the initial metal loading. The HDC reactions in acetate and carbonate buffer solutions also resulted in good conversion rates, while the catalyst activity began to decrease only in the fourth cycle. Buffer medium is an interesting less aggressive alternative for HDC reactions, but still very little exploited

A reação de hidrodescloração (HDC) tem recebido grande atenção como um método de tratamento de resíduos orgânicos mais eficiente que a incineração, especialmente para compostos aromáticos clorados, pois evita a formação de espécies potencialmente tóxicas, como furanos e dioxinas. O presente estudo tem como objetivo a preparação de nanocatalisadores de paládio suportados para a reação de HDC. Buscando facilitar a separação do catalisador do meio reacional e sua reutilização em sucessivas reações foram empregados suportes sólidos com propriedades magnéticas e desenvolvidas estratégias para a imobilização de nanopartículas metálicas nestes suportes. Para isso foi preparado um suporte composto por nanopartículas magnéticas revestidas por uma camada protetora de sílica densa. Os núcleos magnéticos foram preparados pelo método da coprecipitação e em seguida recobertos com sílica pelo método da microemulssão reversa. A estratégia usada para a preparação das nanopartículas de paládio suportadas foi a funcionalização da superfície do suporte, a imobilização do precursor de Pd(II) e a subseqüente redução do metal por hidrogênio em condições brandas. Como resultado foram obtidas nanopartículas de Pd bem dispersas no suporte funcionalizado, sendo que o tamanho de partícula foi dependente do grupo funcional presente no suporte. Suportes funcionalizados com amina e etilenodiamina resultaram em nanopartículas de Pd com diâmetro de 6,4 ± 1,4 nm e 1,3 ± 0,3 nm, respectivamente. Em testes catalíticos de hidrogenação de cicloexeno o catalisador amino-funcionalizado apresentou melhor desempenho com relação ao funcionalizado com etilenodiamina. Para a reação de HDC foram estudadas as melhores condições reacionais para obtenção de uma maior taxa de conversão do substrato, preservando a estrutura do catalisador. Clorobenzeno foi empregado como substrato modelo. Os testes preliminares em diferentes bases e solventes sugeriram que a trietilamina em isopropanol é o melhor meio por resultar em boa conversão de substrato sem alteração significativa na estrutura do suporte após a reação. O lixiviamento dos metais, nos casos estudados, não foi relevante em relação à quantidade de metal presente inicialmente no suporte. As reações em tampão acetato e carbonato também resultaram em boas taxas de conversão, sendo que no teste de reuso o catalisador começou a diminuir a atividade apenas no quarto reciclo. O meio tamponado é uma alternativa interessante por ser menos agressiva, mas ainda muito pouco explorada para a reação de HDC. / The hydrodechlorination reaction (HDC) has received great attention as an alternative treatment of organic residues, which is more efficient than incineration, especially for aromatic organic compounds, and avoids the formation of toxic species, such as furans and dioxins. The present study is focused on the preparation of supported palladium nanocatalysts for HDC. In order to facilitate the separation of the catalyst from the reaction medium and its reuse in successive reactions solid supports with magnetic properties were employed and strategies for the immobilization of metal nanoparticles on the surfaces of these supports were developed. For this purpose a catalyst support comprised of magnetic nanoparticles coated by a protective dense silica layer was developed. The magnetic nuclei were prepared by the co-precipitation method followed by silica coating by a reverse microemulsion. The strategy used for the preparation of supported Pd nanoparticles was first the functionalization of the support surface, immobilization of Pd (II) precursors and than metal reduction by hydrogen under mild conditions. As a result, Pd nanoparticles well-dispersed on the functionalized support were obtained, although the size of the Pd nanoparticles was tuned by the ligand grafted on the support surface. Amine and ethylenediamine functionalized supports formed Pd nanoparticles of 6,4 ± 1,4 nm and 1,3 ± 0,3 nm, respectively. In the catalytic tests of ciclohexene hydrogenation, the amino-functionalized catalyst showed the best performance compared to the ethylenodiamine functionalized support. For the HDC reaction, the most favorable reaction conditions to reach the highest substract conversion rates while preserving the catalyst structure were studied. Chlorobenzene was selected as substrate for the HDC experiments. Initial tests using different bases and solvents suggested that triethylamine in isopropanol are the best conditions for good conversion rates without meaningful change in the support structure after reaction. The metal leaching was negligible in all reactions studied with respect to the initial metal loading. The HDC reactions in acetate and carbonate buffer solutions also resulted in good conversion rates, while the catalyst activity began to decrease only in the fourth cycle. Buffer medium is an interesting less aggressive alternative for HDC reactions, but still very little exploited

Zero-valent metals such as bulk iron and zinc are known to dechlorinate toxicorganic compounds. Enhancement in reaction rates has been achieved through bimetallicnanosized particles such as nickel/iron (Ni/Fe) and palladium/iron (Pd/Fe). Batchdegradation of model compounds, trichlroethylene (TCE) and 2,2'-dichlorobiphenyls(DCB), were conducted using bimetallic Ni/Fe and Pd/Fe nanoparticles. Completedegradation of TCE and DCB is achieved at room temperature. Zero-valent iron, as themajor element, undergoes corrosion to provide hydrogen and electrons for the reductivecatalytic hydrodechlorination reaction. The second dopant metals of nickel and palladium(in nanoscale) act as catalyst for hydrogenation through metal hydride formation thatproduces completely dechlorinated final product. Different compositions of bimetallicNi/Fe and Pd/Fe nanoparticles were synthesized and their reactivity was characterized interms of reaction rate constants, hydrogen generation through iron corrosion, andproducts formation. The observed TCE degradation rate constant was two orders ofmagnitude higher than the bulk iron and nanoiron, indicating that the bimetallicnanoparticles are better materials compared to the monometallic iron systems. Longevitystudy through repeated cycle experiments showed minimum loss of activity. The surfacearea-normalized rate constant was found to have a strong correlation with the hydrogengeneration by iron corrosion reaction. A mathematical model was derived thatincorporates the reaction and Langmuirian-type sorption terms to estimate the intrinsicreaction rate constant and rate-limiting step in the degradation process. Bimetallicnanoparticles were also immobilized into the chitosan matrix for the synthesis of ananocomposite membrane reactor to achieve membrane-phase destruction of chlorinatedorganics under convective flow condition. Formation of uniformly distributed nanosizedparticles is confirmed by high resolution transmission electron microscopy. Themembrane-phase degradation results demonstrated similar trends with the previoussolution phase analysis with the observed enhanced reaction rates. The advantage of themembrane system is its ability to prevent the agglomeration of the nanoparticles in themembrane matrix, to minimize the loss of precious metals into the bulk solution phase,and to prevent the formation of precipitated Fe(III) hydroxide. These are due to thechelating effect of the amine and hydroxyl functional groups in the chitosan backbones.

Orientadores: Antonio Jose Gomez Cobo, Inmaculada Rodriguez Ramos / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-09T18:45:47Z (GMT). No. of bitstreams: 1 Zonetti_PrisciladaCosta_D.pdf: 1969256 bytes, checksum: 26749d2eefdd647b4142060303484744 (MD5) Previous issue date: 2007 / Resumo: Os compostos organoclorados são substâncias químicas que têm como característica uma elevada toxicidade e persistência, tanto no meio ambiente quanto nos organismos vivos. Tal é o caso do pentaclorofenol, usado como herbicida e pesticida na proteção de lavouras e como biocida no tratamento de madeiras e couros. Um método de tratamento bastante promissor é a hidrodescloração catalítica desses compostos empregando catalisadores à base de paládio. Dentro desse contexto, o presente trabalho tem como objetivo principal estudar as condições de preparação de catalisadores Pd/TiO2 e o comportamento dos sistemas bimetálicos Pd-Ni/TiO2, Pd-Ru/TiO2 e Pd-Ti/TiO2. Dentre as variáveis de preparação dos catalisadores Pd/TiO2, foram estudadas as influências do tratamento de ativação, bem como do teor de Pd no sólido sobre o desempenho catalítico. Para tanto, os catalisadores de Pd/TiO2 foram preparados pelo método de impregnação a seco e os catalisadores bimetálicos foram preparados pelo método de co-impregnação. Os sólidos obtidos foram caracterizados por meio das técnicas de adsorção de N2 (BET), análise espectrométrica de raios X (EDX), espectroscopia fotoeletrônica de raios X (XPS), redução à temperatura programada (RTP), espectroscopia no infravermelho da adsorção do CO (FTIR) e microcalorimetria da adsorção do CO. O desempenho dos catalisadores foi avaliado na reação de hidrodescloração do pentaclorofenol, empregandose um reator Parr do tipo "slurry". A reação foi conduzida à pressão de 5 bar e temperatura de 383 K. Os resultados dos testes catalíticos mostram que o catalisador 3%Pd/TiO2 não calcinado e não reduzido permite obter maiores valores para o rendimento e a seletividade de fenol, com uma atividade catalítica relativamente elevada. Os catalisadores bimetálicos com Ni e Ti são seletivos à formação de fenol, enquanto que o catalisador contendo Ru se mostra muito seletivo para a obtenção do cicloexanol, através da hidrogenação do anel benzênico / Abstract: Organic-chlorine compounds are chemicals which main characteristic is high toxicity and persistence, both in live organisms and in the environment. Such is the case of pentachlorophenol, used as herbicide and pesticide for harvest protection and as biocide for treating woods and leathers. A very promising treatment method is the catalytic hydrodechlorination of these products using palladium based catalysts. In this context, the following work is aimed at studying the Pd/TiO2 preparation conditions and the behavior of bimetallic Pd-Ni/TiO2, Pd-Ru/TiO2 and Pd-Ti/TiO2 systems. Within the preparation variables of Pd/TiO2 catalysts, the effects of the activation treatment as well as the influence of Pd content in the solid on the catalysts performance were studied. Therefore, Pd/TiO2 catalysts were prepared by means of the dry impregnation method, and the bimetallic catalysts were prepared by co-impregnation method. The so obtained solids were characterized by the N2 adsorption technique (BET), Xray spectrometry analysis (EDX), X-ray photoelectron spectroscopy (XPS), temperatureprogrammed reduction (TPR), Fourier transformed-infrared spectroscopy of the chemisorbed CO (FTIR) and CO adsorption microcalorimetry. Catalysts performance was evaluated in the entachlorophenol hydrodechlorination reaction using a slurry Parr reactor. The reaction was conducted at 5 bar pressure and at 383 K temperature. Catalytic test results show that the non calcinated and non reduced 3% Pd/TiO2 catalyst allows to attain higher values for yield and for phenol selectivity, with a relatively high catalytic activity. Bimetallic catalysts with Ni and Ti are selective in the phenol formation, while the catalyst with Ru is likely more selective to attain the cyclohexanol by means of the benzene ring hydrogenation / Doutorado / Sistemas de Processos Quimicos e Informatica / Doutor em Engenharia Química

Bifenilas policloradas (PCBs) foram produzidas comercialmente entre 1929 e meados da década de 1980 para propósitos industriais. As mesmas propriedades que despertaram o interesse industrial, tais como: inércia química, alta constante dielétrica, resistência à queima; foram responsáveis pelo espalhamento dos PCBs em todos os compartimentos ambientais, de tal forma que são encontrados em amostras de tecidos adiposos de animais e humanos, leite, sedimentos dentre outras matrizes. Enormes quantidades de PCBs continuam em uso ou estão estocadas a espera de uma destinação final. No presente estudo demonstramos o uso da reação de hidrodescloração catalítica como forma de destruição/destoxificação de bifenilas policloradas. Para tanto, a reação foi estudada em amostras reais de PCBs (óleo dielétrico - Ascarel®), amostras comerciais (Aroclor® 1242 e 1254) e amostra sintética (2,4-diclorobifenila). O estudo se baseia no uso de solventes orgânicos como meio reacional e paládio suportado em carvão ativado como catalisador, devido à sua seletividade para a reação desejada, bem como sua baixa capacidade de hidrogenar compostos aromáticos. xii A condição experimental ótima para a hidrodescloração foi determinada a partir da aplicação de planejamento experimental do tipo Doehlert. Esta condição ótima foi aplicada com sucesso a PCBs contidos em outras matrizes. A cinética da reação é apresentada para o 2,4-diclorobifenila como estudo de caso e uma proposta de mecanismo da reação de hidrodescloração de PCBs é apresentada baseada nos resultados experimentais. / Polychlorinated biphenyls (PCBs) were produced between 1929 and the 1980s for industrial applications. The same properties that make it a chemical of interest for industrial applications, such as: chemical inertness, high dielectric constant, fire resistance; were responsible for the widespreading of PCBs over all enviornmental compartments. They can be found in samples of fat tissues of humans and animals, milk, sediments, among other matrices. Enormous quantities of PCBs are still in use or stocked waiting for a final destination. In the present study, we have shown the use of catalytic hydrodechlorination as an alternative for the destruction/detoxification of polychlorinated biphenyls. For this, the reaction was studied in real samples of PCBs (dielectric oil - Ascarel®), commercial samples (Aroclor® 1242 e 1254) and pure chlorinated biphenyls (2,4-dichlorobiphenyl). The study is based in the use of organic solvents as reactional media and palladium supported in activated carbon as catalyst, due to its selectivity for the desired reaction and to its low capacity to hydrogenate aromatic compounds. xiv The optimal hydrodechlorination condition was determined through the application of a Doehlert experimental planning. This optimal condition was applied with success to PCBs contained in other matrices. The reaction kinetics for 2,4-dichlorobiphenyl was presented as a case study and a mechanistic proposal was presented for the hydrodechlorination of PCBs based on these experimental conditions.

A reação de hidrodescloração catalítica (HDC) de bifenilas policloradas (PCB) foi estudada em diversos sistemas reacionais: solventes orgânicos, dióxido de carbono supercrítico, presença e natureza de aditivos (bases e co-solventes) a temperaturas na faixa de 25 °C a 100 °C e pressões de 1 bar até 250 bar. Os reagentes utilizados foram um composto modelo (2,4- diclorobifenil), misturas comerciais de PCB (Aroclor, Ascarel) e outros compostos halogenados (clorobenzenos e bromoclorobenzeno). Os catalisadores avaliados, paládio suportado em carvão ativo (Pd/C), paládio suportado em sílica mesoporosa (Pd/SiO2), nanopartículas ferromagnéticas de paládio (FFSiNH2Pd), e nanopartículas ocas de paládio (PdNP) e de platina (PtNP), mostraram-se versáteis nas mais diversas condições, quer sejam condições supercríticas, presença ou não de água, presença e natureza da base e diferentes doadores de hidrogênio. Em dióxido de carbono, dois regimes reacionais foram avaliados: dióxido de carbono subcrítico, onde o gás atua como agente expansor da fase líquida ao se dissolver nela permitindo que a reação ocorra em uma fase líquida rica em gás hidrogênio; e dióxido de carbono supercrítico, sistema onde a temperatura influencia fortemente a reação e a pressão tende a ter efeito negativo sobre a velocidade de reação, devido a efeitos de diluição e de competição das moléculas do gás com as moléculas dos reagentes. A condição reacional ótima foi determinada para o regime supercrítico e dados cinéticos foram obtidos para os regimes sub- e supercrítico. / The catalytic hydrodechlorination reaction (HDC) of polychlorinated biphenyls (PCB) was studied in several reactional systems: organic solvents, supercritical carbon dioxide, presence and nature of additives (bases and co-solvents), in temperatures of 25 °C to 100 °C and pressures of 1 bar to 250 bar. The reagents used were: a model compound, 2,4-dichlorobiphenyl, commercial mixtures of PCB (Aroclor, Ascarel) and other halogenated compounds (chlorobenzenes and bromochlorobenzene). The catalysts evaluated, palladium supported in activated carbon (Pd/C), palladium supported in mesoporous silica (Pd/SiO2), palladium ferromagnetic nanoparticles (FFSiNH2Pd), and hollow palladium ((PdNP) and platinum (PtNP) nanoparticles, showed to be versatile in several conditions, either supercritical conditions, presence or not of water, nature of the base, and different hydrogen donors. In carbon dioxide, two reaction regimes were evaluated: subcritical carbon dioxide, where the gas acts as an expansion agent of the liquid phase when it dissolves in it, allowing that the reaction happens in a liquid phase rich in hydrogen; and supercritical carbon dioxide, a system where the temperature has a strong influence over the reaction and the pressure has a negative effect on the rate of the reaction, due to dilution and the competition of gas molecules with the reagents molecules for the catalyst. The optimal reaction condition was determined for the supercritical regime and kinetic data were obtained for both the sub and supercritical regimes.

A reação de hidrodescloração catalítica (HDC) de bifenilas policloradas (PCB) foi estudada em diversos sistemas reacionais: solventes orgânicos, dióxido de carbono supercrítico, presença e natureza de aditivos (bases e co-solventes) a temperaturas na faixa de 25 °C a 100 °C e pressões de 1 bar até 250 bar. Os reagentes utilizados foram um composto modelo (2,4- diclorobifenil), misturas comerciais de PCB (Aroclor, Ascarel) e outros compostos halogenados (clorobenzenos e bromoclorobenzeno). Os catalisadores avaliados, paládio suportado em carvão ativo (Pd/C), paládio suportado em sílica mesoporosa (Pd/SiO2), nanopartículas ferromagnéticas de paládio (FFSiNH2Pd), e nanopartículas ocas de paládio (PdNP) e de platina (PtNP), mostraram-se versáteis nas mais diversas condições, quer sejam condições supercríticas, presença ou não de água, presença e natureza da base e diferentes doadores de hidrogênio. Em dióxido de carbono, dois regimes reacionais foram avaliados: dióxido de carbono subcrítico, onde o gás atua como agente expansor da fase líquida ao se dissolver nela permitindo que a reação ocorra em uma fase líquida rica em gás hidrogênio; e dióxido de carbono supercrítico, sistema onde a temperatura influencia fortemente a reação e a pressão tende a ter efeito negativo sobre a velocidade de reação, devido a efeitos de diluição e de competição das moléculas do gás com as moléculas dos reagentes. A condição reacional ótima foi determinada para o regime supercrítico e dados cinéticos foram obtidos para os regimes sub- e supercrítico. / The catalytic hydrodechlorination reaction (HDC) of polychlorinated biphenyls (PCB) was studied in several reactional systems: organic solvents, supercritical carbon dioxide, presence and nature of additives (bases and co-solvents), in temperatures of 25 °C to 100 °C and pressures of 1 bar to 250 bar. The reagents used were: a model compound, 2,4-dichlorobiphenyl, commercial mixtures of PCB (Aroclor, Ascarel) and other halogenated compounds (chlorobenzenes and bromochlorobenzene). The catalysts evaluated, palladium supported in activated carbon (Pd/C), palladium supported in mesoporous silica (Pd/SiO2), palladium ferromagnetic nanoparticles (FFSiNH2Pd), and hollow palladium ((PdNP) and platinum (PtNP) nanoparticles, showed to be versatile in several conditions, either supercritical conditions, presence or not of water, nature of the base, and different hydrogen donors. In carbon dioxide, two reaction regimes were evaluated: subcritical carbon dioxide, where the gas acts as an expansion agent of the liquid phase when it dissolves in it, allowing that the reaction happens in a liquid phase rich in hydrogen; and supercritical carbon dioxide, a system where the temperature has a strong influence over the reaction and the pressure has a negative effect on the rate of the reaction, due to dilution and the competition of gas molecules with the reagents molecules for the catalyst. The optimal reaction condition was determined for the supercritical regime and kinetic data were obtained for both the sub and supercritical regimes.